State reason for the following:
(i) Lemon is used for restoring the shine of tarnished copper vessels.
(ii) A metal sulphide is converted into its oxide to extract the metal from the sulphide ore.
(iii) Copper wires are used in electrical connections.
State reason for the following:
(i) Lemon is used for restoring the shine of tarnished copper vessels.
(ii) A metal sulphide is converted into its oxide to extract the metal from the sulphide ore.
(iii) Copper wires are used in electrical connections.
(i) Lemon for restoring shine of copper vessels: Copper vessels get tarnished over time due to the formation of a basic copper carbonate layer (or copper(II) oxide, , which is basic in nature). Lemon juice contains citric acid. The acid reacts with this basic layer, dissolving it and restoring the shiny metallic lustre of the copper surface.
(ii) Conversion of metal sulphide to oxide: It is much easier to reduce a metal oxide to its free metal (using reducing agents like carbon or by thermal reduction) than to reduce a metal sulphide directly. Therefore, sulphide ores are first converted into metal oxides before extraction.
(iii) Copper wires in electrical connections: Copper is an excellent conductor of electricity (second only to silver, but much more economical). It is also highly ductile, meaning it can be easily drawn into thin, flexible wires suitable for carrying electric current.
Marking Scheme
- 1State that lemon contains citric acid which reacts with and dissolves the basic copper oxide/carbonate layer to restore shine. (1 mark)
- 2Explain that reducing a metal oxide to its metal is chemically easier than reducing a metal sulphide directly. (1 mark)
- 3State that copper has high electrical conductivity and high ductility, making it ideal for wires. (1 mark)
Hint
Think about the acid-base neutralization for copper tarnishing, the ease of chemical reduction for metallurgy, and the physical properties of copper that make it suitable for carrying current.
Quick Oral Answer
Lemon contains citric acid which dissolves the basic copper oxide layer on the tarnished vessel, exposing the shiny metal underneath. Copper is used for wiring because of its high electrical conductivity and ductility.
Analysis & Explanation
This question tests the practical application of the physical and chemical properties of metals:
- Part (i) relies on the neutralization reaction between the basic oxide/carbonate layer formed on copper and the organic acid (citric acid) present in lemon.
- Part (ii) is a fundamental principle of metallurgy: reduction of oxides is thermodynamically and practically much easier than reduction of sulphides.
- Part (iii) connects the physical properties of copper (high electrical conductivity and high ductility) to its widespread industrial and domestic utility.
Common Mistakes
- 1Writing that copper is the absolute best conductor of electricity (silver is actually the best, but copper is preferred due to cost).
- 2Failing to mention that reducing oxides is easier than reducing sulphides.
Interesting Facts
Silver is the best conductor of electricity, but copper is used globally because it is far cheaper and highly ductile.
A single gram of gold can be drawn into a wire about long due to its extreme ductility!
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2014?
This question carries 3 marks in the CBSE Class 10 Science 2014 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Metals and Non-metals" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Chemical Properties of Metals" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2014 paper?
This is a Short Answer question from Section SECTION-A in the CBSE Class 10 Science 2014 paper.